Around here the new homes have several different methods of piping the secondary condensate drains.
The most noticeable difference is this:
Cheap house: secondary port is left plugged up with the factory plug.
(Pan and switch present also)
Mid to expensive house: secondary port is piped to the exterior over a window or to a pan with a float switch.
I always write up the plugged secondary port as an issue and state that the manuf. recommends it be used.
I looked yesterday in the installers manual for a new Rheem attic unit and found nothing about the condensate drains. It even had a checklist for the installer to use for determining proper installation and nothing there about the condensate lines. The portion of the unit that has the ports had a label that indicated ADP as the manuf. but no manual was there for it.
I have seen units with a clogged main with water ooozing out of the metal joints around the unit. Also remember the humidity that gets blown back into the house when the unit has excess water for prolonged periods.
Is there any code for this except for the catch all that requires the installer to follow the manuf’s specs? It’s hard to use that argument when the manuf’s document is not complete or unavailable on site.